The Skraup synthesis for Quinoline

This is one of the most important methods for preparation of quinoline. In this method the aniline and its derivatives having vacant ortho position is when heated with glycerol, concentrated H2SO4 and an oxidizing agent the resultant product is obtained as quinoline or its derivatives. The nitrobenzene is generally used as mild oxidizing agent in Skraup synthesis. Glycerol when heated with concentrated H2SO4 it gives the acroline after dehydration. Condensation of acroline thus obtained with aniline or its derivatives followed by oxidation gives the quinoline. The reaction is shown follow.

Mechanism:

The step wise mechanism of Skraup synthesis of quinoline is given as follow.